A microcatheter is a catheter that is used for injecting a medicament such as carcinostatic, or the like or a contrast medium (imaging agent) into a peripheral blood vessel of an organ such as a brain, a breast, an abdomen, or the like for practicing procedures such as the diagnosis, treatment, etc., thereof and that is made of an extra fine tube having a diameter of approximately 0.5 to 1.0 mm.
The above microcatheter to be used in a thin curved blood vessel passage is required to be extra fine and is also required to be highly flexible sufficient for inserting and passing it inside a lumen such as a curved blood vessel, etc., without damaging or impairing the blood vessel. On the other hand, since a flexible extra fine microcatheter is easily twisted in a passage having a very small radius, which causes a problem wherein a flow in a lumen may be limited or stemmed. Further, when a microcatheter is moved forward along a passage in a lumen or is made to transmit a torque, the above microcatheter with such an extra fine configuration is not structurally stable, causing a problem that the tube is bent or twisted at various sites along the entire length of the catheter.
For coping with the above problem, for example, PCT Japanese Translation Version 2003-501160 (Patent Document 1) proposes a microcatheter which has, as recited in claims 3 and 4 thereof, (a) an integral tube formed of an inside layer made of materials such as a polyether copolymer, a polyamide copolymer, a fluorine resin, etc., (b) a braid of stainless steel wire formed on the above inside layer for imparting resistance to twisting or preventing the conversion to an elliptical form and further for improving the degree of torque transmission and (c) an outside layer formed of a material comprising a mixture of polyamides as a base material or comprising a polyether and a polyamide as a base material, one of these being a material having a Shore hardness of 70 to 80D, the other being a material having a Shore hardness of 25 to 35D, a distal end portion having a Shore hardness of 25 to 35D, an intermediate portion having a Shore hardness of 25 to 80D and a proximal end portion having a Shore hardness of 70 to 80D, the above outside layer being a layer formed by extrusion of a mixture or formulated material of two materials different in hardness, the compositional ratio of the above two materials being changed during the extrusion so that the hardness of the above integral tube changes along the longitudinal direction.
In the invention of Patent Document I, however, only the hardness is changed without changing the outer dimensions of a shaft tube as shown, for example, in FIGS. 1 to 3. When the forward end diameter of the catheter is decreased, therefore, the diameter of that on the near end side at hand is too small, and even if the hardness of the resin is increased, the tube has only insufficient rigidity. On the other hand, when the diameter on the near end side at hand is increased, the forward end of the catheter is too large, thus involving a problem that the selectivity to a blood vessel is degraded. Further, since the outer layer tube is not continuously coated with same one material and one layer from the end portion near at hand through the forward end portion, there caused a problem that the adhesion to the braid is poor and that the catheter is inferior in pressure resistance and torque performance.
It is an essential basic structural requisite in microcatheter design that the microcatheter has a thin forward end portion (to be also referred to as “distal zone”) and a large base end portion (to be also referred to as “proximal zone”). It is practically difficult to materialize any microcatheter of which the hardness alone is changed without changing outer dimensions of a shaft tube as described in Patent Document 1, and in reality such has not yet been commercialized.
Further, JP 2001-190681A (Patent Document 2) proposes a microcatheter having a catheter body having an inner layer and an outer layer as specified in claim 1 thereof, said outer layer having a first region and a second region that is positioned nearer to the base end side than the first region, said first region being constituted of a polyester elastomer, said second region being composed of a polyurethane elastomer having higher hardness than the polyester elastomer constituting said first region.
In the microcatheter described in Patent Document 2, however, the inner layer is coated with the outer layer formed of two layers, but the innermost layer (first outer layer) of the outer layer is not fully extended up to the forward end of a shaft tube. That is, it is constitutionally cut off in the middle of the shaft tube, so that the problem with the catheter is that the adhesion to a braid is poor and that the microcatheter is inferior in pressure resistance and torque performance.
Further, Japanese Patent No. 2865428 (Patent Document 3) in claim 1 and FIG. 10 and Japanese Patent 2965940 (Patent Document 4) in claim 1 and FIG. 7 describe microcatheters each having a catheter section having a long and narrow tubular member having a proximal end, a distal end and a passage that defines an inside lumen extending between the proximal end and the distal end; the catheter section having (a) a braid member that is a braid of a plurality of ribbons and that is only one reinforcing member having an inside surface and an outside surface, at least most of said ribbons containing an ultra-elastomeric alloy and said braid member extending along at least part of said lumen, (b) at least one polymeric inside lining member inside said braid member, and (c) at least one outside cover member outside said braid member.
However, in the microcatheters described in Patent Document 3 and Patent Document 4, the inner layer formed of two layers is coated with the outer layer formed of two layers, and yet the inner layer (first outer layer) of the outer layer is not fully extended up to the forward end of the shaft tube, either, that is, it is cut off in the middle of the shaft tube, so that, oppositely, the outer layer (second outer layer) of the outer layer is constitutionally extended up to the forward end of the shaft tube. Therefore, these microcatheters have problems similar to those in Patent Document 2.
It is therefore an object of this invention to provide a microcatheter that overcomes the problems of conventional microcatheters having poor adhesion between an outer layer tube and a braid, and being inferior in pressure resistance and torque performance, and that not only improves the pressure resistance of the catheter but also anti-kinking property, thereby making superselective good approach or access of the catheter to a minute blood vessel possible, and also enabling superselective imaging of a blood vessel, administration of dosage and treatment of embolus.